A manufacturing process for a semiconductor device includes a variety of steps such as a lithography step, an etching step and an ion-planting step. After completion of each step and before a shift of the process to the next step, a cleaning step and a drying step are performed for removing impurities and a residue left on a wafer surface so as to clean the wafer surface.
For example, in wafer cleaning treatment after the etching step, a chemical liquid for the cleaning treatment is supplied to the wafer surface, and pure water is then supplied to perform rinsing treatment. After the rinsing treatment, drying treatment is performed in which the pure water left on the wafer surface is removed to dry the wafer.
A known method for performing the drying treatment is, for example, replacing the pure water on the wafer with isopropyl alcohol (IPA) to dry the wafer. However, this method has had a problem of collapse of a pattern formed on the wafer due to surface tension of the liquid during the drying treatment.
In order to solve such a problem, supercritical drying performed with the surface tension being zero has been proposed. For example, inside a chamber, a wafer with its surface wet with IPA is brought into the state of being soaked in carbon dioxide in a supercritical state (supercritical CO2 fluid) so that the IPA on the wafer is dissolved into the supercritical CO2 fluid. Then, the supercritical CO2 fluid with the IPA dissolved therein is gradually discharged from the chamber. Thereafter, a pressure and a temperature inside the chamber are lowered to perform phase transition from the supercritical CO2 fluid to gas, which is then discharged to the outside of the chamber, to dry the wafer.
However, there has been a problem in that, at the time of lowering the pressure inside the chamber to transit the phase of the carbon dioxide from the supercritical state to the gas, the IPA which is left inside the chamber while in the state of being dissolved in the supercritical CO2 fluid is cohered and re-adsorbed onto the wafer, resulting in generation of particles (dried trace). Further, depending on the temperature inside the chamber at the time of the supercritical drying treatment, a metal material constituting an electrode and the like provided on the semiconductor substrate might be etched, thus causing deterioration in electric characteristics of the semiconductor device.